PCNA-dependent long-patch base excision repair (BER) occurs during the S phase of the cell cycle when PCNA and associated DNA polymerases are available. PCNA is part of a large replicative complex that contains DNA polymerase delta or DNA polymerase epsilon, along with RPA and RFC complexes. When POLB (DNA polymerase beta) is unable to excise the oxidatively damaged AP residue (5'ddRP) at the APEX1-generated single strand break (SSB), PCNA and FEN1 are recruited to APEX1, where PCNA interacts with both APEX1 (Dianova et al. 2001) and FEN1 (Tom et al. 2000, Shibata and Nakamura 2002). PCNA-bound DNA polymerase delta complex (POLD) or DNA polymerase epsilon complex (POLE) displaces DNA polymerase beta (POLB) from the SSB (Klungland and Lindahl 1997).